Microstructural characteristics of concrete added with C-S-H and carbon nanotubes

ABSTRACT The incorporation of nanomaterials is a possibility for the improvement and modification of characteristics or properties in materials. The incorporation of nanomaterials is a possibility for the improvement or even the creation of some characteristics or properties in materials. The use of carbon nanotubes (CNT) has been researched in concretes to increase the compressive and flexural strength, modulus of elasticity among other characteristics such as reduced permeability. The aim was to improve the hydration kinetics of cement silicates by creating nucleation spaces and growth of crystalline structures making the microstructure denser, as verified by microscopic analysis and porosimetry. Microconcrete specimens had tensile strength tested at 28 days. The percentages of NTC (0.0% and 0.2%) and C-S-H (0.0% and 2.0%) were varied, as well as the Ca/Si ratio (0.8 and 1.2) of C-S-H. In total, 5 types of composites were produced, and their results were compared to the reference material (without additions). The composite C2-0.8 (with 2% C-S-H of Ca/ Si =0.8) presented tensile strength 18.0% higher than the reference material (R), already for the composite CT2-0, 8 (2% C-S-H Ca / Si = 0.8 and 2% CNT) the increase in resistance of 33% compared to the reference. The composite T2 (added only 0.2% of CNT) presented 13% of increase of resistance when compared to material R. The use of NTC, in concrete or other cementitious mixtures, can be enhanced if used in conjunction with C-S-H (precipitate). This improves the hydration of cement silicates by creating nucleation spaces that favor crystalline growth and reduce porosity as seen in electron microscopy analysis and mercury intrusion porosimetry tests performed on the samples.

摘要
纳米材料掺入法是改善、调控材料各项特征与性能的可行途径，同时还可用于优化甚至赋予材料某些全新的特征与性能。碳纳米管（carbon nanotubes, CNT）已被应用于混凝土的相关研究，以提升其抗压强度、抗折强度与弹性模量等多项性能，同时降低材料的渗透性。本研究通过构建晶核生成位点与晶体生长环境，优化硅酸钙的水化动力学过程，使材料微观结构更致密，该结论已通过显微分析与孔隙率测试得到验证。研究对微混凝土试样开展了28天龄期的抗拉强度测试，变量包括NTC的掺量（0.0%与0.2%）、水化硅酸钙（calcium silicate hydrate, C-S-H）的掺量（0.0%与2.0%），以及C-S-H的钙硅比（0.8与1.2）。本研究共制备了5种复合材料，并将其性能与空白对照组（未添加任何外加剂的基准试样）进行对比。其中，C2-0.8组（掺加2%钙硅比为0.8的C-S-H）的抗拉强度较基准组（R）提升了18.0%；而CT2-0.8组（同时掺加2%钙硅比为0.8的C-S-H与2% CNT）的抗拉强度较基准组提升了33%。仅掺加0.2% CNT的T2组试样，其抗拉强度较基准组R提升了13%。若将NTC与沉淀型C-S-H复掺应用于混凝土或其他胶凝材料体系中，可进一步优化其性能。该复掺体系通过构建利于晶体生长的晶核位点，优化硅酸钙水化过程并降低材料孔隙率，该结论已通过电子显微分析与压汞法孔隙率测试得到验证。